1. Field of the Invention
The present invention relates to a method of manufacturing an electroluminescence (EL) display apparatus, and more particularly to a method of manufacturing an EL display apparatus, in which an EL element is formed on a substrate surface using a mask.
2. Description of Related Art
In recent years, display apparatuses using an EL element have attracted great attention.
Such an EL element may be constituted, for example, by an anode formed by a transparent electrode made of ITO (Indium Tin Oxide) or the like, a hole transporting layer made of MTDATA (4,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)triphenylamine) or TPD (N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-di(3-methylphenyl)-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine), an emissive layer made of BeBq2 (bis(10-hydroxybenzo[h]quinolinato)beryllium) including quinacridone derivative or the like, an electron transporting layer made of BeBq2 or the like, and an electrode (cathode) made of a magnesium indium alloy or the like, which are sequentially accumulated in a laminate structure. In such an EL element, holes injected from the anode and electrons introduced from the cathode are recombined in the emissive layer when a required voltage is applied between these electrodes, to thereby excite organic molecules forming the emissive layer to generate excitons. Through the process in which these excitons radiate until deactivation, the emissive element projects light which is directed externally from the transparent anode through the transparent insulating substrate, whereby desired emission is obtained.
When a display apparatus using such an EL element, i.e. an EL display apparatus, is constituted as a color image display apparatus, the EL display apparatus has a structure of a dot matrix display apparatus in which EL elements each emitting light corresponding to one of three colors, for example, red (R), green (G), and blue (B) are arranged in a matrix. In order to drive these EL elements arranged in a dot matrix pattern, a passive matrix method or an active matrix method can be employed.
In the passive matrix method, the EL elements arranged in a matrix pattern on the display panel to form respective pixels are directly driven externally in synchronization with a scanning signal. In this case, the display region in the display apparatus is constituted only by the EL elements.
In the active matrix method, on the other hand, a pixel driving element (an active element) is provided for each of the EL elements arranged in a matrix to form the respective pixels. The pixel driving element acts as a switch element which switches between on and off states in accordance with a scanning signal. The EL element is driven in such a manner that a data signal (a display signal or a video signal) is transmitted to the anode of the EL element through the pixel driving element which is in the on state, and predetermined current corresponding to the data signal flows between the anode and cathode of the EL element.
For the formation of EL elements used in such a display apparatus, a vacuum evaporation process is often employed. The formation of an EL element using the vacuum evaporation process basically includes the following two steps:
(1) within a vacuum chamber, covering, with a mask, portions of a substrate other than portions where EL elements are to be formed and placing the substrate such that the masked surface faces in the vertically downward direction; and
(2) heating a material for forming the EL element, including a material of an emissive layer or the like, to evaporate the material from under the substrate, thereby depositing the material on the substrate surface and forming the EL element.
In order to form the EL element on the substrate surface in the above-described manner, it is necessary, especially for the formation of the emissive layer, to very accurately align the substrate and the mask. However, if at the time of alignment the substrate is supported in such manner that the EL element forming surface of the substrate constitutes a lower surface which faces downward, it is not possible to dispose this lower surface in direct contact with the mask because most of the lower surface forms the display panel region on which the EL element or the like is to be formed. In other words, it is necessary to support the end portions of the substrate, regions other than the display panel region with an appropriate support hand or the like. When the end portions of the substrate are supported, however, flexure is likely to be generated in the center portion of the substrate. As a result, when the substrate is moved toward the mask side, the center portion of the substrate first comes into contact with the mask. If, under this state, the substrate and the mask are moved relative to each other so as to make alignment, there is a possibility that the film surface of the substrate is damaged, and accurate alignment cannot be obtained.
On the other hand, from the standpoint of the accuracy of alignment and of film deposition, it is desirable to place the substrate and the mask as close to each other as possible, which further exacerbates the above problem.
Further, the above-described problem that flexure in the substrate makes alignment difficult occurs not only with the vacuum evaporation process but also when the EL element is formed by other methods. Therefore, this problem is generally in common in various manufacturing methods as long as accurate alignment is required between the substrate and the mask.
The present invention was conceived in view of the above described problems of the related art and an object of the present invention is to enable more accurate alignment between a mask and a substrate when forming an electroluminescence element using a mask.
In accordance with one aspect of the present invention, there is provided a method of manufacturing an electroluminescence display apparatus, in which, after alignment of a substrate and a mask disposed below the substrate, a material of an electroluminescence element is adhered to the substrate through an opening of the mask to form an electroluminescence element layer, and at least three sides of the substrate are supported by side supporting members at the time of the alignment between the substrate and the mask.
By performing the alignment between the substrate and the mask while the substrate is being supported by the side supporting members as described above, it is possible to inhibit flexure from being generated in the substrate and thereby increase the accuracy of the alignment. It is also possible to prevent the substrate from being bent and contacting the mask or the like disposed below, causing the substrate and the mask to be damaged.
In accordance with another aspect of the present invention, it is preferable that, of the side supporting members, a pair of the side supporting members which support opposing sides of the substrate are symmetrical with respect to each other, at least with respect to a contact and support portion of the side supporting member which contacts and supports the substrate.
When the side supporting members have such a symmetrical feature, in addition to a decrease of the flexure generated in the substrate, it is also possible to support the substrate easily in an even manner. Accordingly, even when the substrate is bent to some extent, it is possible to prevent the substrate being significantly bent in a local region. Thus, the forming conditions of the electroluminescence element layer will not vary, which further prevents significant variation of the display quality within the display region.
In accordance with still another aspect of the present invention, a side portion of a surface of the substrate opposing the mask is disposed on the contact and support portion of the side supporting member. By supporting the substrate in this manner, the substrate can be supported reliably with a simple structure.
In accordance with a further aspect of the present invention, the mask is fixed and positioned with respect to mask frames which are arranged at intervals each being larger than the length of a portion of the substrate in the side direction which is supported by the contact and support portion of the side supporting member, and, after the mask which has been positioned and the substrate which is supported by the side supporting members are aligned with each other, the side supporting members are withdrawn or removed from positions on the substrate where the side supporting members support the substrate, through the intervals of the mask frames.
The mask frames on which the mask is positioned thus include the intervals which do not interfere with the motion of the side supporting members, so that the side supporting members can be withdrawn quickly without unintentionally touching the substrate and the mask. This makes it possible to reliably accommodate a need, if any, for removing the side supporting members at the time of the formation of the electroluminescence element layer.
In accordance with another aspect of the present invention, the mask is fixed and positioned with respect to a mask frame, after the mask which has been positioned and the substrate which is supported by the side supporting members are aligned with each other, the side supporting members are withdrawn, and, subsequently, an electroluminescence element layer is formed on a lower surface of the substrate while the substrate is being supported on at least one of the mask and the mask frame.
Here, in accordance with still another aspect of the present invention, the mask frame may be disposed on a holding plate, and the mask, the mask frame, or the holding plate may comprise pins for supporting the substrate thereon.
When an electroluminescnece element layer is formed after the side supporting members are withdrawn, by supporting the substrate by the mask, the mask frame or the like, it is possible to prevent the flexure generated in the substrate at the time of formation of this element layer, which leads to an increase of the accuracy of formation of the element layer and also to an improvement of the quality of a display apparatus. Further, supporting of the substrate by means of the mask, the mask frame, or the holding plate can be achieved using a simple structure such as the above-described pins.
In accordance with another aspect of the present invention, the mask is fixed and positioned with respect to a mask frame, and the mask which has been positioned and the substrate are aligned with each other, with the substrate being supported by the side supporting members and a plurality of pins provided on the mask or on the mask frame.
In accordance with still another aspect of the present invention, the alignment between the mask and the substrate is performed while the substrate is being supported by the side supporting members and an electrostatic adsorption member for adsorbing an upper surface of the substrate by means of electrostatic force.
As described above, in addition to the side supporting members, a further supporting mechanism is employed during alignment, so that the flexure in the substrate generated at the time of alignment can be still more reliably prevented.
In accordance with another aspect of the present invention, at least the alignment between the substrate and the mask may be performed within a vacuum chamber. Further, the vacuum chamber may be an evaporation chamber for the electroluminescence element layer, for example.
As described above, even when the alignment of the substrate is carried out within a vacuum chamber or the like, it is possible to reliably support the substrate using a combination of the side supporting members and the pins or an electrostatic adsorption member or the like.